The present invention relates to an electromagnetic metering valve for a fuel injector, in particular for internal combustion engines.
Fuel injector metering valves normally comprise a control chamber having a discharge conduit closed by a shutter with the aid of a main spring; and the shutter is opened by energizing an electromagnet to overcome the action of the spring.
To reduce rebound of the arrested mass when the valve is closed, it has been proposed to disconnect the armature from the stem and provide a second spring by which the armature is pushed against the stem.
In one known metering valve in which the stem is guided by a fixed sleeve, the armature must be allowed fairly ample overtravel with respect to the stem to enable the armature to be fitted to the stem once the stem is inserted inside the fixed sleeve.
To reduce the time interval between two consecutive operations of the armaturexe2x80x94as required, for example, in multiple-injection engines, i.e. with injection systems capable of multiple injections in each cylinder at each combustion cyclexe2x80x94it has been proposed to minimize the overtravel of the armature with respect to the stem by fitting a C-shaped bush to the stem after it is connected to the armature.
The bush has the drawback of not being locked positively in its seat and therefore becoming unseated. Also, not being secured axially, the bush tends, in use, to oscillate together with, and so prolong oscillation of the armature.
It is an object of the invention to provide a metering valve of the above type, which is highly straightforward and reliable, provides for eliminating the aforementioned drawbacks typically associated with known valves, and provides for rapid arrest of the armature in the valve opening position.
According to the present invention, there is provided an electromagnetic metering valve for a fuel injector, comprising a shutter for a discharge conduit of a control chamber, an electromagnet for activating an armature to control said shutter via an intermediate member, and a first spring acting on said intermediate member to keep said shutter in the closed position; said armature being disconnected from said intermediate member and being pushed against the intermediate member by a second spring; and stop means, independent of said shutter, being provided to arrest the movement of said armature produced by said first spring so as to reduce the overtravel of said armature with respect to the travel of said intermediate member; characterized in that said stop means comprise at least one plate which is locked transversely with respect to said intermediate member.
More specifically, the plate is locked transversely by a fastening member of the electromagnet, and is kept resting elastically against a fixed stop by said second spring.